Re: [PATCH] erofs: use the opener's credential when verifing metadata accesses

[Christoph Hellwig <hch@infradead.org>]

On Fri, May 08, 2026 at 05:10:21PM +0800, Gao Xiang wrote:
> On the one side, I hope if there could be some interface for
> such temporary usage rather than just one vfs_iter_read model.

As in a in-kernel mmap?  While not entirely impossible, the locking
model for that sounds horrible.

> > Now for reads it mostly works on the most common disk-based file systems,
> > but it does create lots of problem for slightly more complex ones like
> > network/clustered or synthetic file systems.  It also really breaks
> 
> Just out of curiousity, could you point out one specific path
> so I can look into that.

file system might require their own locking, e.g. cluster locks for
cluster file systems, and at least in the path direct page cache access
also caused problems with NFS data invalidation semantics.  Last but not
least ->read_folio has a file paramater that isn't really a file but a
file system specific cookie.  So calling this with something not managed
by the file system can cause problems as has caused crashes in the past,
although the offender at that time (the old smbfs) is now gone.

> But could we just fix this issue first for previous linux versions?

I just pointed out another issue.  You'll have to fix the credentials
either way.